Doomsday scenario

A doomsday scenario is a story of how we might meet our horrible end as a species, or even how the Earth might be destroyed. These range from the mythical, to the silly, to the paranoid, to the scientific.

A new virus/bacteria/parasiteevolves and eliminates mankind (not exactly doomsday because life will go on. Also has to get around the fact that there exists an inverse relationship between ease of transfer and death rates percentage.)